1. Field of the Invention
The present invention relates to a wafer loading and unloading mechanism, and more particularly relates to a wafer loading and unloading mechanism which is provided in a loading robot composing an automatic single-wafer single-side polishing machine for picking up wafers inserted in loading cassettes.
2. Description of the Related Art
Generally, an automatic single-wafer single-side polishing machine is constructed in such a way that wafers are stored once in a device called a "loading robot" before being delivered to a buffer unit for polishing.
The loading robot of this type is provided with a pair of storage portions for wafers, called "loading cassettes", in the upper part thereof, and is constructed in such a way that a plurality of unpolished wafers are stored piled in one of a pair of loading cassettes without contacting each other and are delivered successively to a buffer unit by a grabbing means, and then polished wafers are stored successively piled again by a grabbing means in a loading cassette disposed on the other side without contacting each other.
In this arrangement, unpolished wafers stored piled in one of the loading cassettes are to be stored piled in the other loading cassette after being polished.
The loading robot as described above includes two operating members for ensuring a grabbing operation made by a grabbing means, a first operating member moving the loading cassettes upward and downward, and a second operating member swinging the loading cassette in such a way that the rear side of the loading cassette (viewed in the direction of wafer insertion) moves upward with the front side thereof (viewed in the direction of wafer insertion) as a fulcrum in order to place each wafer in the loading cassettes in the same position in plan view.
Generally, since the operating member for moving the loading cassettes upward and downward is so constructed that it transmits driving force from a drive via a belt, the sliding movement of the belt during transmission of driving force inevitably generates fine particles from the belt or causes dust to become airborne, and even worse, the belt is located above the wafers. Therefore, this has a disadvantage in that if the polished wafers are contaminated by fine particles or dust due to the sliding movement of the belt, the wafers will be deemed to be defective, and thus productive efficiency decreases.